Answer to Question #157681 in Biology for Anas Bajbouj

Question #157681

Part II: Describe the process of DNA replication in complete sentences?

Expert's answer

The first step in DNA replication is to unwind the double helix structure of the DNA molecule via helicases. The separation of the strands forms a Y-like shape structure called a replication fork. The two separated strands serve as templates for making the new copies of DNA. One of the strands is oriented in the 3’ to 5’ direction (the leading strand). The other strand is oriented in the 5’ to 3’ direction (the lagging strand). At the leading strand, a short piece of RNA (primer) is made by the enzyme primase. The primer acts as the starting point for DNA synthesis. The enzyme DNA polymerase binds to the leading strand and moves along the DNA strand starting from the primer. It attaches a new complementary nucleotide to the growing strand of DNA in the 5’ to 3’ direction. At the lagging strand, numerous RNA primers are made by the primase while DNA polymerase provides the elongation of these primers. These short DNA fragments, called Okazaki fragments, are then added to the lagging strand also in the 5’ to 3’ direction. Next, exonuclease strips away the rimers while the gaps between them are filled with complementary nucleotides via DNA polymerases. Finally, DNA ligase joins DNA fragments together. As a result, the DNA replication process results in the formation of two DNA molecules.

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